In this paper, the thermo-viscoplastic behaviour of DH-36 and Weldox-460-E steels is analyzed at wide ranges of strain rates and temperature. These materials are commonly used for naval applications. Thus, the may be subjected to a wide range of exploitation temperature and at the same time to high strain rates due to accidental impact or explosion. The thermo-viscoplastic behaviour of these materials has been modeled by application of RK (Rusinek-Klepaczko) constitutive relation. The comparison with other models well known in the literature has been studied.

In this paper the thermo-visco-plastic behaviour of six high strength steels is analyzed in a wide range of strain rates and temperature. The steels belong to two well-known versions of steels: three ferritic steels: HSLA-65, DH-36 and Wedox 460-E and three austenitic steels: Nitronic-50, Uranus B66 and Al-6XN.
Micro-mechanism of plastic deformation in the case of ferritic steels is dominated by dislocation's gliding. In the case of austenitic steels the twinning appears that modifies the material's plastic properties. In the present paper the RK (Rusinek-Klepaczko) constitutive relation is evaluated for modelling of the plastic behaviour of six steels which represent these two different deformation mechanisms.

In this paper an extension of the Rusinek-Klepaczko (RK) constitutive relation is presented. The new formulation proposed, allows defining the phase transformation effect observed on macroscopic scale using a phenomenological approach. The key point is to introduce in the original formulation of RK model a new stress component based on evolution of martensite, which takes into account strain, strain rate and temperature effects. Analytical predictions of the xtended constitutive relation are compared with experimental results for 301Ln2B steel.

A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method permits determination of the rate-sensitive plastic properties of materials up to strain rate∼105s−1. Miniaturization of the experimental setup with specimen dimensions: diameter dS=2.0 mm and thicknesslS=1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain, makes possible compression tests at strain rates from∼103s−1to∼105s−1. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar (SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10−4s−1to5*104s−1. A diabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress versus the logarithm of strain rate and they show two regions of a constant rate sensitivity β¼Δσ.log": relatively low up to the strainrate threshold∼50 s−1, and relatively high above the threshold, up to strain rate∼4.5*104s−1.